Re: [patch]: fixing of pmtimer overflow that make Cx states time incorrect

alex.shi
2009-02-01T10:03:15Z

On Sun, 2009-02-01 at 10:04 +0800, Zhao, Yakui wrote:
> On Tue, 2009-01-27 at 14:52 +0800, Andrew Morton wrote:
> > The fix looks reasonable to me.
> >
> > Please always cc linux-acpi@vger.kernel.org on acpi patches.
> >
> > The patch was quite a mess: inlined code plus an attachment, mangled
> > email headers, funny characters in the email body, 300-column lines,
> > etc.
> >
> > I reproduce a cleaned up copy below.
> Thanks for the clean up.
> But it seems that there exists a potential overflow.
> In the clean-up patch the data type of idle_time is defined as u32.
> And the idle_time will be converted to sleep_tick by using the macro
> definition of US_TO_PM_TIMER.
> >#define US_TO_PM_TIMER_TICKS(t) ((t*(PM_TIMER_FREQUENCY/1000))/1000)
> If the idle_time is more than 4.687s, the overflow will happen.
> So the interval variable(idle_time) had better be defined as 64-bit
> type.
>
> In fact the following patch is already updated based on the Venki's
> suggestion.
> The monotonic time is not required while getting the C-state sleep
> state. In such case the function of ktime_get_real is enough
>
> thanks.
>
yes, this kind of overflow will cause a little Cx sleep time omit. So we
try to use s64 bit idle_time to present the Cx sleep time. For this
purpose we need to use div64_u64 to convert US_TO_PM_TICKS in i386
mode. So we rewrite this patch on 2.6.29-rc3 as following. Please revert
previous version before patch it.

Alex
> It's a bit odd that several of these functions (for example,
> acpi_idle_enter_bm()) return number-of-microseconds in a plain `int'.
> It should be an unsigned scalar - `unsigned int', `u32', `u64', etc.

>
> Also, all those functions have kerneldoc comments, but none of them
> document the function's return value, which is a rather important part
> of the interface!
>
> Oh well.
>
>
>
> From: Alex Shi <alex.shi@intel.com>
>
> We found Cx states time abnormal in our some of machines which have 16
> LCPUs, the C0 take too many time while system is really idle when
kernel
> enabled tickless and highres. powertop output is below:
>
> PowerTOP version 1.9 (C) 2007 Intel Corporation
>
> Cn Avg residency P-states (frequencies)
> C0 (cpu running) (40.5%) 2.53 Ghz 0.0%
> C1 0.0ms ( 0.0%) 2.53 Ghz 0.0%
> C2 128.8ms (59.5%) 2.40 Ghz 0.0%
> 1.60 Ghz 100.0%
>
>
> Wakeups-from-idle per second : 4.7 interval: 20.0s
> no ACPI power usage estimate available
>
> Top causes for wakeups:
> 41.4% ( 24.9) <interrupt> : extra timer interrupt
> 20.2% ( 12.2) <kernel core> : usb_hcd_poll_rh_status
(rh_timer_func)
>
>
> After tacking detailed for this issue, Yakui and I find it is due to
24
> bit PM timer overflows when some of cpu sleep more than 4 seconds.
With
> tickless kernel, the CPU want to sleep as much as possible when system
> idle. But the Cx sleep time are recorded by pmtimer which length is
> determined by BIOS. The current Cx time was gotten in the following
> function from driver/acpi/processor_idle.c:
>
> static inline u32 ticks_elapsed(u32 t1, u32 t2)
> {
> if (t2 >= t1)
> return (t2 - t1);
> else if (!(acpi_gbl_FADT.flags & ACPI_FADT_32BIT_TIMER))
> return (((0x00FFFFFF - t1) + t2) & 0x00FFFFFF);
> else
> return ((0xFFFFFFFF - t1) + t2);
> }
>
> If pmtimer is 24 bits and it take 5 seconds from t1 to t2, in above
> function, just about 1 seconds ticks was recorded. So the Cx time
will be
> reduced about 4 seconds. and this is why we see above powertop
output.
>
>
> To resolve this problem, Yakui and I use ktime_get() to record the Cx
> states time instead of PM timer as the following patch. the patch was
> tested with i386/x86_64 modes on several platforms. and the Cx states
> time become good. this patch do not fully remove PM timer for Cx idle
> time recording. Maybe it can be recovered if the PM timer get
improved in
> hardware.

Signed-off-by: Alex Shi <alex.shi@intel.com>
Signed-off-by: Yakui.zhao <yakui.zhao@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
Index: linux-2.6.29-rc3/drivers/acpi/processor_idle.c
===================================================================
--- linux-2.6.29-rc3.orig/drivers/acpi/processor_idle.c
+++ linux-2.6.29-rc3/drivers/acpi/processor_idle.c
@@ -64,7 +64,8 @@
#define _COMPONENT ACPI_PROCESSOR_COMPONENT
ACPI_MODULE_NAME("processor_idle");
#define ACPI_PROCESSOR_FILE_POWER "power"
-#define US_TO_PM_TIMER_TICKS(t) ((t * (PM_TIMER_FREQUENCY/1000)) / 1000)
+#define US_TO_PM_TIMER_TICKS(t) div64_u64(\
+ (t * (PM_TIMER_FREQUENCY/1000)), 1000ULL)
#define PM_TIMER_TICK_NS (1000000000ULL/PM_TIMER_FREQUENCY)
#ifndef CONFIG_CPU_IDLE
#define C2_OVERHEAD 4 /* 1us (3.579 ticks per us) */
@@ -396,8 +397,9 @@ static void acpi_processor_idle(void)
struct acpi_processor *pr = NULL;
struct acpi_processor_cx *cx = NULL;
struct acpi_processor_cx *next_state = NULL;
- int sleep_ticks = 0;
- u32 t1, t2 = 0;
+ s64 sleep_ticks = 0;
+ ktime_t kt1, kt2;
+ s64 idle_time;

/*
* Interrupts must be disabled during bus mastering calculations and
@@ -544,14 +546,15 @@ static void acpi_processor_idle(void)

case ACPI_STATE_C2:
/* Get start time (ticks) */
- t1 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ kt1 = ktime_get_real();
/* Tell the scheduler that we are going deep-idle: */
sched_clock_idle_sleep_event();
/* Invoke C2 */
acpi_state_timer_broadcast(pr, cx, 1);
acpi_cstate_enter(cx);
/* Get end time (ticks) */
- t2 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ kt2 = ktime_get_real();
+ idle_time = ktime_to_us(ktime_sub(kt2, kt1));

#if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86)
/* TSC halts in C2, so notify users */
@@ -559,7 +562,7 @@ static void acpi_processor_idle(void)
mark_tsc_unstable("possible TSC halt in C2");
#endif
/* Compute time (ticks) that we were actually asleep */
- sleep_ticks = ticks_elapsed(t1, t2);
+ sleep_ticks = US_TO_PM_TIMER_TICKS(idle_time);

/* Tell the scheduler how much we idled: */
sched_clock_idle_wakeup_event(sleep_ticks*PM_TIMER_TICK_NS);
@@ -605,13 +608,14 @@ static void acpi_processor_idle(void)
}

/* Get start time (ticks) */
- t1 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ kt1 = ktime_get_real();
/* Invoke C3 */
/* Tell the scheduler that we are going deep-idle: */
sched_clock_idle_sleep_event();
acpi_cstate_enter(cx);
/* Get end time (ticks) */
- t2 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ kt2 = ktime_get_real();
+ idle_time = ktime_to_us(ktime_sub(kt2, kt1));
if (pr->flags.bm_check && pr->flags.bm_control) {
/* Enable bus master arbitration */
atomic_dec(&c3_cpu_count);
@@ -624,7 +628,7 @@ static void acpi_processor_idle(void)
mark_tsc_unstable("TSC halts in C3");
#endif
/* Compute time (ticks) that we were actually asleep */
- sleep_ticks = ticks_elapsed(t1, t2);
+ sleep_ticks = US_TO_PM_TIMER_TICKS(idle_time);
/* Tell the scheduler how much we idled: */
sched_clock_idle_wakeup_event(sleep_ticks*PM_TIMER_TICK_NS);

@@ -1455,7 +1459,8 @@ static inline void acpi_idle_do_entry(st
static int acpi_idle_enter_c1(struct cpuidle_device *dev,
struct cpuidle_state *state)
{
- u32 t1, t2;
+ ktime_t kt1, kt2;
+ s64 idle_time;
struct acpi_processor *pr;
struct acpi_processor_cx *cx = cpuidle_get_statedata(state);

@@ -1476,14 +1481,15 @@ static int acpi_idle_enter_c1(struct cpu
if (pr->flags.bm_check)
acpi_idle_update_bm_rld(pr, cx);

- t1 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ kt1 = ktime_get_real();
acpi_idle_do_entry(cx);
- t2 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ kt2 = ktime_get_real();
+ idle_time = ktime_to_us(ktime_sub(kt2, kt1));

local_irq_enable();
cx->usage++;

- return ticks_elapsed_in_us(t1, t2);
+ return idle_time;
}

/**
@@ -1496,8 +1502,9 @@ static int acpi_idle_enter_simple(struct
{
struct acpi_processor *pr;
struct acpi_processor_cx *cx = cpuidle_get_statedata(state);
- u32 t1, t2;
- int sleep_ticks = 0;
+ ktime_t kt1, kt2;
+ s64 idle_time;
+ s64 sleep_ticks = 0;

pr = __get_cpu_var(processors);

@@ -1533,18 +1540,19 @@ static int acpi_idle_enter_simple(struct
if (cx->type == ACPI_STATE_C3)
ACPI_FLUSH_CPU_CACHE();

- t1 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ kt1 = ktime_get_real();
/* Tell the scheduler that we are going deep-idle: */
sched_clock_idle_sleep_event();
acpi_idle_do_entry(cx);
- t2 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ kt2 = ktime_get_real();
+ idle_time = ktime_to_us(ktime_sub(kt2, kt1));

#if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86)
/* TSC could halt in idle, so notify users */
if (tsc_halts_in_c(cx->type))
mark_tsc_unstable("TSC halts in idle");;
#endif
- sleep_ticks = ticks_elapsed(t1, t2);
+ sleep_ticks = US_TO_PM_TIMER_TICKS(idle_time);

/* Tell the scheduler how much we idled: */
sched_clock_idle_wakeup_event(sleep_ticks*PM_TIMER_TICK_NS);
@@ -1556,7 +1564,7 @@ static int acpi_idle_enter_simple(struct

acpi_state_timer_broadcast(pr, cx, 0);
cx->time += sleep_ticks;
- return ticks_elapsed_in_us(t1, t2);
+ return idle_time;
}

static int c3_cpu_count;
@@ -1574,8 +1582,9 @@ static int acpi_idle_enter_bm(struct cpu
{
struct acpi_processor *pr;
struct acpi_processor_cx *cx = cpuidle_get_statedata(state);
- u32 t1, t2;
- int sleep_ticks = 0;
+ ktime_t kt1, kt2;
+ s64 idle_time;
+ s64 sleep_ticks = 0;

pr = __get_cpu_var(processors);

@@ -1644,9 +1653,10 @@ static int acpi_idle_enter_bm(struct cpu
ACPI_FLUSH_CPU_CACHE();
}

- t1 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ kt1 = ktime_get_real();
acpi_idle_do_entry(cx);
- t2 = inl(acpi_gbl_FADT.xpm_timer_block.address);
+ kt2 = ktime_get_real();
+ idle_time = ktime_to_us(ktime_sub(kt2, kt1));

/* Re-enable bus master arbitration */
if (pr->flags.bm_check && pr->flags.bm_control) {
@@ -1661,7 +1671,7 @@ static int acpi_idle_enter_bm(struct cpu
if (tsc_halts_in_c(ACPI_STATE_C3))
mark_tsc_unstable("TSC halts in idle");
#endif
- sleep_ticks = ticks_elapsed(t1, t2);
+ sleep_ticks = US_TO_PM_TIMER_TICKS(idle_time);
/* Tell the scheduler how much we idled: */
sched_clock_idle_wakeup_event(sleep_ticks*PM_TIMER_TICK_NS);

@@ -1672,7 +1682,7 @@ static int acpi_idle_enter_bm(struct cpu